Circuit breakers for interrupting an electrical circuit, i.e. discontinuing flow of electrical current in the electrical circuit, are known. Such circuit breakers are arranged in the respective electrical circuits which are intended to be interrupted based on some predefined event occurring in the electrical circuit. Generally, operation of such circuit breakers are responsive to detection of a fault condition or fault current. On detection of such a fault condition or fault current, a mechanism may operate the circuit breaker so as to interrupt the current flowing therethrough, thereby interrupting the current flowing in the electrical circuit. Typically, once a fault is detected, contacts within the circuit breaker separate in order to interrupt the electrical circuit. Often spring arrangements, pneumatic arrangements or some other means utilizing mechanically stored energy are employed to separate the contacts. Some of the energy required for separating the contacts may be obtained from the fault current itself. When interrupting the current flowing in the electrical circuit, an arc is generally generated. This arc must be cooled so that it becomes quenched or extinguished, such that the gap between the contacts repeatedly can withstand the voltage in the electrical circuit. It is known to use vacuum, air, oil or insulating gas as medium in which the arc forms. Insulating gas comprises for example sulphur hexafluoride, SF6, gas. Once the fault condition has been mitigated or eliminated the contacts are closed, whereby flow of current in the electrical circuit can be resumed.
The circuit breaker contacts should be able to carry the load current without excessive heating. Also, the circuit breaker contacts should be capable of withstanding heat of the arc that is produced when the electrical circuit is interrupted. Contacts are for example made of metals or metal alloys such as Cu or Ag or alloys containing Cu and/or Ag. The cooling and/or extinguishing or the arc may take place in a component of the circuit breaker often referred to as a puffer-type cylinder or selfblast chamber. Such a puffer-type cylinder is typically connected to the electrical circuit at two ends via respective current path sections, often referred to as the upper and lower current paths or current path sections. In general, the maximum possible continuous rated current for a circuit breaker is limited by the choice of material in the current carrying parts in the circuit breaker.
There is an ever increasing demand for circuit breakers having higher maximum continuous rated current.
In order to increase the maximum possible rated continuous current for a circuit breaker, it has been proposed to increase the cross section of current path sections so as to obtain a decrease in the resistance of the current path sections. However, by the arrangement of the current paths sections relatively to the puffer-type cylinder, such a solution may require increasing the diameter of the puffer-type cylinder. Hence, such a solution may entail relatively high costs.
It has also been proposed to equip the circuit breaker with an additional puffer-type cylinder arranged in parallel to the existing puffer-type cylinder in order to achieve a larger surface via which cooling can be effected.
Hence, proposed solutions may entail substantial modification of existing equipment. It would be desirable to be able to increase the maximum possible rated continuous current for a circuit breaker while requiring only relatively small modification of existing equipment.